Disavowing a redirected domain?

Following some drops during the recent spam updates I've been taking a closer look at backlinks, and found that someone has 301 redirected a couple of domains into my clients site.

The backlinks pointing at these domains are entirely spam – so the upshot is I now how have thousands of spam backlinks pointing at my clients site via 301 redirect.

I know the general Google view is that these links will just be ignored but I don't really trust that to be true/foolproof – especially given recent declines that coincide with the spam updates.

Obviously I don't own the domains that are redirecting so I can't just turn the 301 off – so can I just add a couple of lines to my disavow file to disavow the domains that are redirecting – or will I need to disavow all of the backlinks that point to the redirecting domains?