BI source system data refresh

Guru's,

My source system for my BI QA environment is being refreshed, all new data will be in the source system.

My question is this: Do I have to delete all data in BI QA environment to ensure that my source and target systems match? Also, what are the steps for deleting all data from BI?

I know I have to delete the transactoin data before I can delete the Master data, but was wondering if there was such a thing as a mass delete of Master Data in BI.

Thanks.