How to correctly write an MDX expression for a set

Hello, 

i've got 2 dimension hierarchies:

1) [Hierarchy1].[CityOfBirth]

2) [Hierarchy2].[CityOfResidence]

Both these hierarchies contain same members - cities

How do I write an MDX expression for a set containing all possible combinations of both dimensions ([Hierarchy1].[CityOfBirth].Member, [Hierarchy2].[CityOfResidence].Member) but excluding those tuples where [Hierarchy1].[CityOfBirth].Member = [Hierarchy2].[CityOfResidence].Member.

I.e. there shouldn't be tuples like (New York, New York) or (Chicago, Chicago) in the set.