Domain Access is a great Drupal module for setting acces to content (nodes) depending on the (sub-)domain.
It has great integration with Views but there a few caveats though, one of them is that it can be quite hard to make a Views display that shows content from multiple domains. There are two options that I know of:
- Add a Special Page Request on the Domain Settings page
- Disable SQL rewriting
Both have their own merits.