We all have pages that, without warning, fall out of favor in Google and we've all been frustrated in trying to figure out why. Google won't tell you why a page suddenly receives zero visitors and it's clear, since Panda/Penguin, that pages can work against the rest of your site. This being the case I'm trying to be pro-active with a plan.
Using Google analytics I set up a method of identifying pages that receive no traffic from search within a given 14 day period and these are automatically moved into a category on my site reserved for news type articles. Articles that aren't meant to be a challenge to my top page for any given keyword. All articles within this category have a google noindex meta tag applied.
The result is that if Google isn't sending traffic the article is de-indexed where I can either leave it that way or modify it and send it back into circulation. I mean, if Google won't send traffic to it and it *might* be working against the rest of my site it should be deindexed, right?
I think moving content to another domain or a subdomain will only work if the original domain no longer links to that content.
@claaarky there's something in what you say. It sounds logical to me and it could be the reason why they haven't escaped Panda. Today, I checked and saw that they have already switched back their subdomains to to their root domain. So, it wasn't a good practice anyway.