Compare one gridview against another gridview... Is that possible?

 I'm working on a project for HR where I have two gridviews.  The first gridview (gvCurrentEmp) has a list of SSN, Names, and date of hire for Current Employees.  The 2nd gridview(gvPreviousEmp) has a list of SSN, Names and date of hire for Previous Employees.  On the chance that they mis-typed the SSN or there is a duplicate, they'd like me to check the SSN's in the 1st gridview, against the SSN's in the 2nd gridview.  And, if there is a match between, I need to highlight the SSN in both gridviews.  I figured out how to do the highlight, but how to I compare all the rows of one gridview against all the rows in another gridview? 
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