My page blocks cache is invalidated and I would like to clear it; however, nothing appears broken and I'm unsure what can happen if I do and don't have a backup of what's cached. I would appreciate any insight you might have.
If you made changes to pages/blocks, it can cause this message to appear. It's not a real 'error' - as in nothing is really 'broken' - but closer to a reminder. Try not to clear cache too often (for performance reasons), but it is safe to refresh periodically when required.