I am creating notebooks which usually get edited. I then want to evaluate the newly saved notebook but I want it to be evaluated from scratch and not use data which I had created in the previous version during the current session. However,  I have noticed that the new notebook does not work well because it seems that the data associated with the previously run notebook is not cleared. I want to rerun the notebook after saving a new version and have it be evaluated from scratch.  The only way this work is for me to exit Mathematica, restart it , reload the notebook and then evaluate the notebook in the new Mathematica session. This seems clearly inefficient. My question is how to reevaluate the changed, saved notebook from scratch? I have tried putting a 'clear all' as the first line but this does not seem to throw away all data, etc from the previous evaluation.  Can you guys please clue me in. I feel this is a very basic question and am embarrassed to ask, but need a better way.

Thanks very much!

Comer