HPCC-11637 Add some tracing to the log when cache is rebuilt

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6122 from ghalliday/issue11637

HPCC-11637 Add some tracing to the log when cache is rebuilt

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>