roycerus - 6:12 pm on Apr 15, 2013 (gmt 0)
Something like this happened to us where we got millions of pages indexed by error. I was advised to remove the robots.txt block and redirect those requests [301 permanent] to a 410 Gone.
The pages are still getting removed after 4 months and we are starting to see slight upward trend. I think there has to be a PR update to reshuffle the PR juice so the pages on the domain get their valid share [for us].