How many detail grids could one have in a master detail setup?

I have 2 detail grids with a master but are having some problems with data loading/unloading in the last grid.

grid structure

master

detail grid #1 (parent is master)

detail grid #2 (parent is detail #2)

My problem is, when changing the selection in the master the detail grid #1 is updated but how do I clear the data in detail grid #2 which is no longer current. I have tried loadComplete and gridComplete options in grid #1 where i try to update the data in grid #2.

Please help as I realy don't know how to solve this issue.