How to manually fire IDataErrorInfo validation on all TabItems - MVVM

Question

I am using MVVM pattern, my application is basically TabControl with 3 TabItems with DataGrids inside them.

I can save all data from grids to csv files and load it back. I try to add functionality that after user clicks button, a new window of string collection with all DataGrids validation errors pops out. I almost succeeded but I find out that I have to click through all TabItems to fire up their IDateErrorInfo property validation and gather the strings.

So my question is how can I manually fire the validation of specific tab from code? I tried something like jump through all tabs with SelectedIndex property of TabControl in loop firing PropertyChanged("SelectedIndex") each time and it changes the tab but doesn't fire validation and I get errors only from last, now visible tab.

EDIT

More details:

My every tab has its own ViewModel with ObservableCollection<[TabModel]> connected to DataGrid. All 3 TabModels have implemented IDataErrorInfo interface. Every tab has own xaml file and all these files are gathered in MainWindows.xaml's TabControl like this:

<TabControl SelectedIndex="{Binding SelectedTab, UpdateSourceTrigger=PropertyChanged}">

        <TabItem Width="auto" Header="FOO" Name="Foo">
            <Controls:Foo DataContext="{Binding FooVM}"/>
        </TabItem>
        ...
</TabControl>

In Foo.xaml I have simple DataGrid with columns and validation turned on on specific column, i.e.:

<DataGridTextColumn Header="ID" Binding="{Binding Id, ValidatesOnDataErrors=True}"/>

In every TabModel I have List<string> Errors to which I add every result from IDataErrorInfo public string this[string name]

I try to get/do all validation from MainWindowVM's code position.