Syntax for Non-US Contacts

I have a report displayed on the master account detail page that shows all contacts associated with that master account. This includes contacts with locations both national and international. If you drill down on the location of the contact, you are redirected to a report that shows all contacts at that specific location. Currently, this only works for US contact addresses. I was hoping someone could provide me with the proper formula to use that will show this report with non-US contacts included. Right now, if you drill down on an international address, you are met with an error message.