load datagrid ItemsSource from a Page to a Window

I am developing an application which uses NavigationWindow as follows

1. NavigationWindow as Mainwindow

2. Page0.xaml which has a 2 datagrid's (dgMaster and dgDetail) in Master Detail scenairo.   

3.Window1.xaml which will be displayed as ShowDialog() on dgDetails's Row_DoubleClick's event setter as follows

<DataGrid.ItemContainerStyle><Style TargetType="DataGridRow"><EventSetter Event="MouseDoubleClick" Handler="Row_DoubleClick"/>                                </Style></DataGrid.ItemContainerStyle>

public void Row_DoubleClick(object sender, RoutedEventArgs e)
 {
  Window1 my_Window = new Window1();
  my_Window.ShowDialog();
  }

for point number 2, the code snippet is as follows

// on datagrid row selection changed, it should load the ItemsSource in the Window1 datagrid. dg3 is the datagrid in Window1. 
private void dgDetails_SelectionChanged(object sender, SelectionChangedEventArgs e)
 {
 this.db = new testDB_Entities();
 string IDMapper = (dgDetails.SelectedItem as Details).Name;
 var Query1 = from a in this.db.Details
                   orderby a.ID == IDMapper
                   select a;
 dg3.DataContext = null;
 dg3.DataContext = Query1;
 dg3.Items.Refresh();
  }

the above codes together displays the window in form of a dialog box but the datagrid is empty.

how to load the ItemsSource of the datagrid in Window1.xaml from the Page0.xaml.

I understand that these controls belong separately to each xaml files, but is there a way to display a controls datacontext from another xaml ( regardless a page /window).

if anybody dont understand the question. please let me know.. i will try to explain it better. Thanks in advance