I've been through this process a few times. You have it mostly right, except for #4. I corrected it below.
1. turn host into maintenance mode.
2. drop existing diskgroups ( evacuate data ).
3. upgrade firmware
4. power cycle the computer. That is to say power off, then power back on. A reboot will not work.
5. secure erase disk
6. recreate diskgroups
Excuse the use of my personal VMware account and not the one from my employer (micron) for the user name.