condiationate calculated member and total

hi all,

I have a question regarding total on a calculated member

here is what I write :

WITH MEMBER [Measures].[Test] as IIF(Not Instr([Dimention].[Attribut].CurrentMember.Member_caption,[Dimension2].[Attribut2].CurrentMember.Member_caption)>0,[Measures].[Mymeasure],Null)

It works good on detail line, but I don't know how to have a good result (only displayed sum) on dimension totals and grand total.

Thanks for your help