I contact a slew of domain owners, hosts and registrars each day both via e-mail and telephone, to get domains/IPs cleaned, suspended or completely nuked. The vast majority generally go something like this;

1. Contact domain owner/host/registrar
2. Report what was found

In the case of domain owners, I typically also have to give advise on what's needed as far as getting it cleaned up and secured, and of course, reported to LE (i.e. who to contact and what they'll typically ask for).

The vast majority of the domain owners are grateful that I've taken the time to report it to them, and help them get everything sorted out. Hosting companies and registrars typically either don't respond, or respond with an auto-response - with some following up to let me know what they've done (i.e. cleaned up or suspended). Indeed, I'm working with several registrars and hosts on various cases on an on-going basis.