Group 1:
If persons going to india/China after getting GC/Citizenship - May not be considered as brain drain.... they might have left for pleassure( think ing better life in india )/personal reasons
Group 2:
If persons are going back to INDIA/China due to - Lack of GC/Visa Issues/Did not find Job/Citizenship/Better Technology/Better opportunities - might be considered in brain drain flock.
In my experience... I never heared chinese IT prefessional went back to China !!!