As of npm@5, the npm cache self-heals from corruption issues and data extracted from the cache is guaranteed to be valid. If you want to make sure everything is consistent, use npm cache verify instead. On the other hand, if you're debugging an issue with the installer, you can use npm install --cache /tmp/empty-cache to use a temporary cache instead of nuking the actual one.
If you're sure you want to delete the entire cache, rerun:
npm cache clean --force
A complete log of this run can be found in /Users/USERNAME/.npm/_logs/2019-01-08T21_29_30_811Z-debug.log.