Query ASH for Undo Blocks

there is a plan with an Index Range scan that generates way more buffer_gets than you would expect.
Would it be correct to query active session history using CURRENT_FILE#  and CURRENT_BLOCK# to check against DBA_EXTENTS to find out if some buffer gets are coming from undo? The query does work, but i am not sure if the result is showing the indented answer.

Thanks

Lothar

--
http://www.freelists.org/webpage/oracle-l