Interesting, it rarely happens but once indexed this creates a minor challenge to make sure it's removed from the results and replaced with your non https:// results - all without losing any ranking.

There's two options which come to mind.

All search engines allow a special file called "robots.txt" to be placed in the root of your web site. You'll need to serve a different robots.txt for SSL versus normal - The basic way to do this is using your .htaccess or web.config rewrite rules - Something like:

RewriteCond %{SERVER_PORT} ^443$
RewriteRule ^robots.txt$ robots_ssl.txt

Another option would be in your rewrite rules to use a 301 redirect if the User Agent is a search engine bot (for example GoogleBot is google's). 301 redirects mean the page is permamently replaced with a new location.

The Robots.txt file, if by chance you aren't familiar with it, has a basic intro at http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=156449

Good luck, please comment for further questions and I'll update this post with more details if needed.