Most ISPs submit their domestic ranges voluntarily to certain blocklists, e.g. the Spamhaus PBL.

I used to have a bunch of blocklist services in my MTA configuration, with different lists having different weights and so on. Eventually it became clear to me that nearly all true spam that hit any one list would also hit Spamhaus Zen. So I scrapped my list of lists, and relied entirely on Zen. My life became easier.

Note: Zen includes the PBL; so if you block using Zen, then you will block mail from domestic ranges. Zen is pretty safe (unless you are expecting mail from domestic ranges). It's safest to use Zen as part of a scoring system, with something like Spamassassin to add heuristic content scoring.