Your observations are correct, the syncing is one way from the Protect server to the Distribution Servers. You could attempt to create a Custom Action that could delete files from these shares. Once created, you could scan the servers that contain the Distribution Server (agentless scans) and then run the Custom Action against the machine to remove the contents from the share. This would require the Distribution Shares to be in the same locations on each server.
The Custom Action would be similar to this How To Remove The Propatches Folder Using Custom Actions in Protect 9.1
You would need to figure out what works best for Step 4.
These document should help:
I would also suggest submitting a quick feature request: Feature Request
Let me know if you have any questions.
Thank you I have put in a feature request