Drush cc all 'Killed'
The string "Killed" doesn't exist in the Drupal 6.30 codebase.

You might have a custom/contrib module which is responsible, or perhaps a Drush extension.

If that's the case, to find it:

grep -nr "Killed" /path/to/drupal/root
grep -nr "Killed" /path/to/drush/extension/folder


(The extension path will probably be ~/.drush)