Calling a Command on Parent from Child

I have a Page:

 <ContentPage  x:Name="MyPage">

The Page references an external xaml via a resource

<ResourceDictionary Source="SomeTemplate.xaml"></ResourceDictionary>

All is fine, but in the external xaml I am trying to reference a **MyPage ** command, but **MyPage ** can't be found - the compiler throws an errors.

<SomeControl TappedCommand="{Binding Source={x:Reference MyPage}, Path=BindingContext.SomeCommand}">