Here's what you can do. Go to
http://www.hcidata.com/host2ip.htm
and look up the host/domain from the IP address. Use whois to find the domain registrar's tech contact. You can also use abuse.org & try a lookup for an abuse e-mail for the domain. Send a
polite note asking about the port scanning.
If you don't get a reposne, sign the tech contact up for porn site e-mail mailing lists. That'll get their attention. (just kidding)