I am not sure where Memex local storage is located. Doesn't seem to be under chrome://extensions.
Here are the instructions I was unable to follow:
Then on “local storage” and delete the 3 items related to google. Then reload the extension (disable/enable)
I have been using the extension for a few hours and find myself constantly adding sites to the blacklist. Have you thought about implementing a whitelist instead? Let the user to opt-in what sites they want indexing. I have seen others also commented on security concerns because of financial or health institution sites are captured by default. I would think a whitelist would be much easier to implement than trying to figure out what needs to be on the default blacklist?