How can I prevent users seeing activities about other users from a different territory?

How can I prevent users seeing activities about other users from a different territory?

Hi,

We have a territory called 'Circle Crimson & Co' and another called 'Australia' - the users in these territories have the same role (in this case, core consultants), but I do not want them to be able to see what the other territory is doing. Currently Circle Crimson & Co users can see Australia user's contacts, companies and activities. Please let me know which permissions I need to change to stop this happening.

Thanks,
Nicole