title: Detecting reference to cell from other workbooks?
body: <p>Is there a way with VBA and/or some formula in Excel to check whether there are other workbooks/sheets referencing a cell? Ideally, also from which workbooks/sheets but if this is not possible, that's also ok. </p>
  
  <p>Lets say I have a workbook with a list of proxy addresses, I want to know if a proxy is already being used by checking if there's any other workbook  referencing its cell. This is to have an indicator whether it's a free proxy or already in use.</p>
  
  <p>Any alternative solution that's close to this is also welcome. I'm not per se looking for a full blown solution, but I can get far by pointing me in the right direction. </p>