My client's instance is one workspace shared with all regions globally (not ideal I know).
We have created a Revenue Model for Australia, and set the assignment rules to only move leads to the Known stage if their Country/Inferred Country is Australia. However it looks like anyone who fills out any form is appearing in the Known stage. Is it possible to restrict leads who enter a Revenue Model?
Sure, just add that restriction to the transitions or entry campaigns.
Country=Australia or IS NOT Australia.
Are you running several RCMs? You must ensure that each one is mutually exclusive.