A word of caution on this:
> 1. completely wipe the flash, data and spare area
>   

We found that forcing erasure of bad block markers on Micron MLC FLASH 
part (29F32G08QAA) left the block in a state where it could not be 
programmed again (i.e. the bad block marker could not be set again).  
This is fair enough - there are no guarantees from the manufacturer that 
bad blocks can be reprogrammed if erased.

At the time we did this as we had a h/w problem that was making our s/w 
think good blocks were bad; having corrected the h/w issue we wanted to 
recover all the incorrectly marked bad blocks.

We ended up replacing the FLASH parts on the afflicted boards.

To address this issue properly I think the only choice is to program a 
bad block table into a working block; I would guess only one block would 
need to be sacrificed, but deciding which block to use and which layer 
to implement such a thing at would require more time and effort than it 
is perhaps worth - just don't erase bad blocks!

Hope this helps,
Robin