First it should be clarified that, in general, it is not possible to enforce someone to purge data, since you never know who has modified their software or has made additional copies of the data elsewhere. This is not a specific problem with blockchains.
Having said that, presumably you want a mechanism whereby all nodes are informed that they should purge some data, and they then report back confirming that they have done so.
If so, we would recommend using a separate stream for this, in which one node can give an instruction to delete some data. At the application level, other nodes check for these instructions (perhaps comparing their publisher against the original item's publisher address) and then post an additional stream item to confirm when the purging is done.
Would that work?
