Creating a Subset based on attributes from two different dimensions

[hydrojoe]

I'm trying to learn how to create a dynamic subset that is based on two different dimensions' attributes. Please check out my example below and offer advice if you can please. Thanks  ;D

Dimensions 
Dept 
Account

Let's say the attributes are called 'Valid' and the value i'm looking for is "Yes" for both of those dimensions.

In essence I want to write a MDX expression possibly to create a dynamic subset that would give me all Dept's with the attribute of Yes that would be based on all the Accounts with the attribute of Yes. Does that make sense?