Using count() and crossjoin() to return distinct counts

[ariesnw]

In my AS cube, I've created a calculated measure using the following MDX:
Count(Crossjoin({[Measures].[Number of hits]},
Descendants([Area].Currentmember, [Area].[User Name])),
Excludeempty)
As expected, the measure provides the number of unique users for each area visited (based on logs from a web site). The problem I'm having is that the total number of unique users for ALL areas visited appears to be the sum of the
unique users from each area, rather than simply being the total number of unique users. Anyone have any suggestions on how to get the cube to calculate correctly at the ALL level?