I have answered this in your ‘other’ topic, avast ‘can’t’ repair corrupt files, it isn’t a function of avast.
Scanning a specific area has nothing to do with what I would call thorough as the Sensitivity setting would determine that. There are three sensitivity settings, Quick, Standard and guess what Thorough. So there you have your answer, Thorough is the most thorough of scans, add to that you can also select Archives to be scanned. But don’t expect it to be a fast scan.
Thorough is also by its design very thorough (it scans all files) and perhaps a little overkill for routine use, were a Standard scan without archives should be adequate. Archive (zip, rar, etc.) files are by their nature are inert, you need to extract the files and then you have to run them to be a threat. Long before that happens avast’s Standard Shield should have scanned them and before an executable is run that is scanned.
I have only ever done a Through Scan with Archives once shortly after installation just to ensure a clean start state, but with XP for example avast will do a boot-time scan after installation if you select it, this I believe will be quicker and reasonably effective. Like everything in life things are a compromise.