wpf, Button to check a checkbox, while the checkbox IsChecked is bound to something else

I have a button lives in View1. View1 has ViewModel1. I have a CheckBox that lives in View2. View2 has ViewModel2. Now if I wanted to use a button command to check the Checkbox (Note that the CheckBox IsChecked is already bound to something else). So just for practicing and try to make it work, I made a class called Commands like shown below. then I made another class called CommandsViewModel as shown below, that will be used by the button to show a MessageBox. Now how to make it check the CheckedBox to instead of showing the MessageBox.

Here is the Commands Class

public class Commands : ICommand
{
    Action<object> executeMethod;
    Func<object, bool> canExecuteMethod;

    public Commands(Action<object> executeMethod, Func<object, bool> canExecuteMethod)
    {
        this.executeMethod = executeMethod;
        this.canExecuteMethod = canExecuteMethod;
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public void Execute(object parameter)
    {
        executeMethod(parameter);
    }

    public event EventHandler CanExecuteChanged;
}

Here is the CommadsViewModel Class

public class CommandsViewModel
{
    public ICommand MyCommand { get; set; }
    public CommandsViewModel()
    {
        MyCommand = new Commands(ExecuteMethod, canExecuteMethod);
    }

    private bool canExecuteMethod(object parameter)
    {
        return true;
    }

    private void ExecuteMethod(object parameter)
    {
        MessageBox.Show("Command executed!");
    }
}

Here is the button

<Button Content="Select All"
       Command="{Binding MyCommand, Source={StaticResource cmdvm}}"
       MinWidth="150" Margin="0,5,20,20">

Here is the Checkbox

<CheckBox
        Name="myCB"
        Content="{Binding ItemName}" 
        IsChecked="{Binding ItemIsChecked}"/>