I'd just warn that most domain forwarding ends up returning a 301 response code anyway, and some return a 302. You could always test it out to see what happens. I checked (non-masked) domain forwarding on two hosts and found 301s in the header in both cases. I believe this is fairly common.

One controversial solution might be a JavaScript redirect that search engines can't understand instead. It's obviously cloaking if the content is different, but maybe not if the content is similar. See https://support.google.com/webmasters/answer/2721217?hl=en&ref_topic=2371375

Unfortunately, there's not a redirect method that would prevent both versions of the site from being indexed. Even with a penalty, the old site could out-rank the new one for branded and long-tail traffic.

Perhaps the best/safest option is to simply noindex/nofollow the pages, then show a warning with a link to the new version of the page. Yes, it requires a new click from users, but it's simple enough that there's little to worry about.

Hi,

So you did add a meta noindex tag? Great. Remember that Google needs to crawl the page to see the meta noindex, so blocking it in robots.txt will mean it's still indexed, but has about 0% chance to show up in search unless you search for that URL.

Also, I wouldn't spend any time worrying about obscure pages that are indexed. It's not going to hurt your rankings.

I typically tell people not to worry about these types of sites. EVERYONE gets a little spam linkage, and it's rarely worth worrying about.

If you have been hit with a manual penalty or think you're being impacted by Penguin already, then yes, definitely include these domains in the disavow list. Technically Google wants you to try to have the links removed first.

First off, make sure your site has not been compromised. Are there sections on your site where users generate their own content? Are the links pointing to spam comments or pages you didn't create? Spammers whose sites Google has already banned will often hack or otherwise compromise a site and use it as a gateway to their site. More on that from Google here:

http://support.google.com/webmasters/bin/answer.py?hl=en&answer=163634

Next, if you're not dealing in anything like the anchor text indicates, don't worry about it. Spam attacks are generally ineffective, and this is especially true when they're completely different from the terms on the page or the terms you seem to want to rank for.

Really, this is probably not worth worrying about. I wouldn't disavow unless you think it's negatively impacting your site, or unless you have had a warning from Google Webmaster Tools.