WInvoice Validation by OU

We are implementing Multi-Org and where will now have one operating unit, we will shortly have two. After the first of the year we will add a few more, Payables loads a number or invoices into Payables via excel spreadsheet and they want some validation in place which indicates that the invoices in being loaded to the correct OU. The spreadsheet has a field where OU is designated, but since the OU is user selected they want some other safeguard. If it is determined the invoice is coded to the wrong OU on the spreadsheet, I don't think there is