Ghost Post?

Very, very annoying. And odds are, this question probably won’t get answered for another 3 years, but here’s the deal: I made a post for testing purposes on one of my categories, added the feed for this specific category in my primary sidebar widget, deleted the post because it looked tacky, and it’s still there. Deleted it out of trash, still there.

Resaved RSS widget, still there. Deleted widget and replaced, still there. Cleared all posts, rebuilt categories, still there. My feed for this category reflects a new post everywhere else but this widget. UGH. Can I clear some sort of internal cache to get rid of this? It’s very frustrating. Thanks.