Hi Jeremy,
You're right, I've just remembered this note in the workflow documentation:
For example, deleting a recipient via a workflow will not result in all of the recipient's delivery history being deleted. However, deleting a recipient directly in the 'Recipients' folder will indeed result in all data linked with this recipient being deleted.
So purging the folder is the right solution. However, I'm not sure if the ClearFolder function is really purging the data or simply removing the data from the folder but without deleting it from the database.
Have you tried other syntax? In the JSAPI, the ClearFolder function seems to only need the folder ID as parameter, so maybe something like ClearFolder("869848332")
If this is not a syntax problem, then I don't know any other similar function available to purge recipient data, so doing it manually would be the only way.
Florent