compare two columns and delete unique from one

Ok,

I have a table on sheet1 with lot numbers in coulmn A.
This table changes via an external datasource.

On sheet2, I have values in column A taken from the column A on sheet1, and in column B some comments on that specific lot.

What I would like to do, is as the data on sheet1 is updated;

compare column A on sheet1 with column A on sheet2 and delete any rows on sheet2 that contain a unique value in column A (meaning the vlaue is no longer valid in my external datasource.... and would no longer be present in column A on sheet1.

I have seen a lot of macros for deleting duplicates, but really non that are working for this issue.

sktneer,
I'm not the one you posted this for, but it is exactly what I was looking for and it works perfect. So thank you from me, since the other person wouldn't thank you for your time.