public class ViewModel : OnPropertyChangedClass
    {
        private int _value = 10;

        public int Value { get => _value; set { _value = value; OnPropertyChanged(nameof(Value)); } }

    }

<UserControl x:Name="userControl"
             x:Class="CyberForum.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="180" d:DesignWidth="160">
    <Grid>
        <TextBlock  Text="{Binding Value, ElementName=userControl}"/>
    </Grid>
</UserControl>

    public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }

        public int MinValue { get; } = 5;


        public static readonly DependencyProperty ValueProperty =
            DependencyProperty.Register
            (
                nameof(Value), 
                typeof(int),
                typeof(UserControl1),
                new FrameworkPropertyMetadata(0, ValuePropertyChanged,ValuePropertyValidate)
            );

        public int Value
        {
            get { return (int)GetValue(ValueProperty); }
            set { SetValue(ValueProperty, value); }
        }

        private static void ValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            /// Для установки точки останова
            /// при отладке
        }

        private static object ValuePropertyValidate(DependencyObject d, object e)
        {
            UserControl1 x = (UserControl1)d;
            int newValue = (int)e;

            if (newValue < x.MinValue)
                return x.MinValue;

            return newValue;
        }
    }

    <Window.DataContext>
        <local:ViewModel/>
    </Window.DataContext>
    <StackPanel>
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="UserContol     " Margin="10"/>
            <local:UserControl1 x:Name="uc" Margin="10" Value="{Binding Value, Mode=TwoWay}"/>
        </StackPanel>
        <TextBlock Margin="10">
            <Run Text="Значение из ViewModel:"/>
            <Run Text="{Binding Value}"/>
        </TextBlock>
        <TextBlock Margin="10">
            <Run Text="Значение из UserControl:"/>
            <Run Text="{Binding Value, ElementName=uc}"/>
        </TextBlock>

        <StackPanel Orientation="Horizontal">
            <TextBlock Text="Новое значение" Margin="10"/>
            <TextBox Width="50" x:Name="tb" Margin="10"/>
        <Button Content="Записать в UserControl новое значение" Click="Bt_Click" Margin="10"/>
        </StackPanel>
    </StackPanel>

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

        }

        private void Bt_Click(object sender, RoutedEventArgs e)
        {
            if (int.TryParse(tb.Text, out int value))
                uc.Value = value;
        }
    }

GetBindingExpression(ValueProperty)?.UpdateSource();

        private static void ValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            /// Для установки точки останова
            /// при отладке
            BindingOperations.GetBindingExpression(d, ValueProperty)?.UpdateSource();
        }

        private static object ValuePropertyValidate(DependencyObject d, object e)
        {
            UserControl1 x = (UserControl1)d;
            int newValue = (int)e;

            if (newValue < x.MinValue)
            {
                 BindingOperations.GetBindingExpression(d, ValueProperty)?.UpdateSource();
                return x.MinValue;
            }
            BindingOperations.GetBindingExpression(d, ValueProperty)?.UpdateSource();

            return newValue;
        }

        private static object ValuePropertyValidate(DependencyObject d, object e)
        {
            UserControl1 x = (UserControl1)d;
            int newValue = (int)e;

            if (newValue < x.MinValue)
            {
                x.Value = x.MinValue;
                return x.MinValue;
            }

            return newValue;
        }