Filtering URL lists

I have scraped a list of URL's to use with a blog commenting application, but I want to exclude all duplicate URLS, without having to trim the URL down to just the root...i.e.

something.com/cool_page.html
something.com/cool_page56.html
another.com/anotherpage.html
another.com/anotherpage56.html

I would want to ditch the 2nd and 4th URL so I am only left with 1 result from each domain. I have a URL washer which i found on this forum that will give me

something.com
another.com

But not the whole URL for the 2 domains....does anyone have any ideas on how to clean large url lists of duplicate root domains?

Cheers