There is much discussion going on about Google's proposed tool to disavow links, but Bing is a step ahead and has already launched theirs.
Sign into Bing Webmaster Tools, click on the "configure my site site" tab and then select
"Disavow Links".
There are options to discount links from a domain, a directory or a page. All you need to do is indicate which you want, and then enter the url and click "Disavow".
I feel sure that Google will now follow with their own tool very soon.