So, I moved /etc/workflow/instances to /tmp/foo. Created sling:Folder, /etc/workflow/instances. And Recursively Deleted /tmp/foo (through /crx Content Explorer).
- There could be RUNNING or STALE workflow. You really need to remove COMPLETED workflows only.
- When you create new /etc/workflow/instances sling:Folder, you need jcr:mixinTypes = ["rep:AccessControllable"]
- and, set sling:resourceType = cq/workflow/components/instances
There is http://dev.day.com/content/kb/home/cq5/CQ5SystemAdministration/howtopurgewf.html
But use it with caution. It can kill the instance.