DBMS_SCHEDULER.PURGE_LOG

begin

   dbms_scheduler.purge_log (
      log_history => 0,                     -- Number of days to keep (0 deletes everything)
      which_log   =>'JOB_AND_WINDOW_LOG',   -- JOB_LOG, WINDOW_LOG or JOB_AND_WINDOW_LOG
      job_name    => null                   -- Delete logs specific to a given job.
   );

end;
/