The fix for 6624765 was putback but part of the fix caused nightly testing
failures and was backed out under 6665445. This CR is to investigate the
backed out code (which cleaned the card table for the expanded part of
the generation and some flavor of it is needed for a complete fix).
Cleaning the newly committed pages was cleaning pages in another
committed region. Limit the pages being committed to pages not
in another committed. See comments for additional details.