Use MVVM With UserControl

Question

I'm trying to make a UserControl which has it's own Viewmodel.

I used dp to pass parameter from View to my UserControl.

public object SelectedItemCliEnt
{
    get { return (object)GetValue(SelectedItemEntProperty); }
    set { SetValue(SelectedItemEntProperty, value); }
}
public static readonly DependencyProperty SelectedItemEntProperty =
    DependencyProperty.Register("SelectedItemCliEnt", typeof(object),
        typeof(UCComboBoxClient), new PropertyMetadata(null));

Now, in my user control I bound the datagrid SelectedItem to this property:

<DataGrid x:Name="dtg_entite"
      ItemsSource="{Binding CliColl, Source={StaticResource vm}}">
    <DataGrid.SelectedItem>
        <MultiBinding Converter="{StaticResource MultiBinding}"
                      Mode="TwoWay">
            <Binding Path="SelectedCli"
                     Source="{StaticResource vm}"
                     Mode="TwoWay" />

            <Binding Path="SelectedItemCliEnt"
                     Mode="TwoWay"
                     RelativeSource="{RelativeSource AncestorType={x:Type UC:UCComboBoxClient}, Mode=FindAncestor}" />
        </MultiBinding>
    </DataGrid.SelectedItem>
</DataGrid>

I also bound the selectedItem to a property (SelectedCli) in my ViewModel which I can access by using a resources, it allow me to modify the content of the datagrid:

<ViewModel:VMUCCBClient x:Key="vm" />

How can I notify to SelectedItemCliEnt the changes in SelectedCli from the UserControl's ViewModel?