Understanding Agency Partitioning
When agency partitioning is turned on, only the records in your agency are displayed in search results. However, you still might be able to see some records from another agency if the records are connected to records that are not partitioned. For example, if Incident records are partitioned, but Name records are not, then if a Name record is connected to an Incident record from another agency, you'll still be able to see the Incident record after opening the Name record.
Records are automatically partitioned by agency. Any time someone in your agency creates a record, it is assigned to your agency. Even administrators can't create records for other agencies. However, administrators can choose to see records from other agencies if they change the Agency field filter on the Search page. The only exception is the Dispatch screen, which is automatically filtered by agency for all users. As an administrator, use the Call History screen to search for Call records from another agency if needed.
Also, if a specific user needs to view all records, regardless of agency, then an admin can indicate that on the User record for that person. If your User record has been marked as able to view all records, then even if agency partitioning is turned on, you'll be able to see records from all agencies.