If you did and if the search engine is Google, you will have a chance at removing those indexed feeds or content.
I never thought of this procedure until I read the following post on Google's Google webmaster central blog.
Earlier I thought that if my robots.txt or robots meta tag would take care of all that But now I have access to a new tool. A tool that let me withdraw pages slipped through those barriers.
But the following article takes you through every step of removing a web page that got indexed by mistake. I hope other search engines will pick a clue and provide the same to webmasters.
Now where did that feed go!
Official Google Webmaster Central Blog: Requesting removal of content from our index