Ok, I am not an expert on this, and I might have an incorrect mental model, but there are a few different things when people refer to "Cache".
I believe the Cache you are referring to, available using Internal Storage, or maybe Manage Apps, is the cached files or settings of applications.
I could be wrong, but I think, the System Cache is something totally different. This would be the settings used by the operating system itself.
When you do an update, the person creating the update assumes a clean phone, no apps downloaded, the general distribution of operating system and applications (both those that accompany Android, and those accompanying a network/carrier's version). Problem is, your device is not this same clean test environment. And not all the settings in your version of Android map cleanly to the version you are trying to install.
In my experience, flaky operation post-update may require a system cache wipe, and if necessary, an FDR.
I suppose you could also clear the application caches.
Personally? I prefer to backup just my photos and any downloaded content. I perform an FDR. I re-download just what I need, and reconfigure those apps. It's a chance to get rid of useless stuff and start fresh. The hardest part of this for most people is getting their email back on line, but many of the email apps these days can set themselves to use the proper protocols and authentication after you provide the email address and the password (which hopefully you remember or have written down).
Hope I got this right.
I have never gotten a corrupt OTA. Ever. The OTA is designed I believe to check itself before initiating the update process. So to have to use another tool to re-install the OTA is something I've never personally had to do. YMMV.
