Some Organizations are part of a Chain and all Chains have the option of turning on a feature called "Global Accounts". This feature will allow your Organizations to share Accounts and Contacts across the whole Chain.

With this feature turned on you will see Accounts in your list that may not have been created at your property. There is currently no filter to sort these by which Property owns them but you can add a Column for "Organization" which will show you which Organization created that Account.

Utilizing a Picklist Custom Field (e.g. "Account Organization" or something similar) for Accounts would allow you to filter by that if you would like to build in this functionality.