ComboBox ItemsSource to parent collection binding

usercountrol.xaml

<!-- In user countrol resources -->
    <UserControl.Resources>
        <CollectionViewSource Source="{Binding Currencies}" x:Key="Currencies"/>
    </UserControl.Resources>

<!-- below inside ex. DataGrid -->
  <ComboBox ItemsSource="{Binding Source={StaticResource Currencies}}" IsSynchronizedWithCurrentItem="False"
            DisplayMemberPath="IsoCode"
            SelectedItem="{Binding BaseCurrency}"/>

<!-- IsSynchronizedWithCurrentItem="False" is important, otherwise ComboBoxes will select same item for each child viewmodel -->