1. Stop scrapers by blocking certain countries. A lot of webmasters find China and the Ukraine are the worst offenders, YMMV.
2. Stop search engines keeping a cached copy of your content, likewise the Wayback Machine. This means scrapers will have to come direct to you to do the thieving.
3. Who is buying the Adsense ads on the infringing sites, and how do they feel about supporting plagiarism? It may not hurt to contact them directly and ask.