[throwawayqq]

So, say Big Corp. in the US calls out a company located in another country for patent infringement in their SaaS that is being used by US users, where Big Corp have their territory patent. Are you saying the international company can be sued by the US company? Where would they even sue them since they are not US based and other countries commonly don't acknowledge other countries' IP and laws?

[lucozade]

If Big Corp has a US patent and Inter Corp is infringing in the US then Big Corp can take them to a US court. If they win then either Inter desists in the US or pays a licence fee (or whatever the court decides).

The fact that Inter Corp is incorporated somewhere else is irrelevant as it's its operation in the US that will be brought to book. Outside of the US it's a different matter and will depend on what international patents Big Corp has, where Inter Corp is infringing etc.