I don't trust the "delete" button to scrub it from FB's database.

I'd be slightly more confident (slightly) that editing the post might cause the core data in the db to be updated, however. In which case, I think the more effective script would be one that goes through all of your FB posts and scrambles them, or replaces the text with gibberish.

If you use Reddit and want to delete your comment/post history I would recommend Shreddit[0] for the reason you mentioned[1]. It's important to do this frequently because there are quite a few sites out there that cache Reddit content periodically.

[0] https://github.com/x89/Shreddit

[1] https://www.reddit.com/r/blog/comments/1dhw2j/reddits_privac...