Removing redundant url's from search engines

Old url's

[damienhandslip]

I have a number of URL's which are either dead or where they have been replaced by new domain names or sub domains. What is the quickest way of deleting them from the search engines.
I can't use robot.txt as I no longer have the original web space in some cases.

[sgaze]

If you have no access to the original web space, I think it's impossible. If not, you will be able to remove from SE the sites of you competitors too!