Create the separate custom field Activity’s record subsidiary in the activity records. Since entity field are differnt in all activity records due to this reason
Source the subsidiary of the entity to the custom field
Create separate saved searches for subsidiaries to restrict the results of activity records based on the Subsidiary.
Defined the roles who will see search results as their view of the selected record type, in lists
In role record, checked the restrict checkbox under the searches Subtab to restrict the other saved search in the list view