Not something I have looked at before, but it should be very easy to test/verify.
From the description I would expect there are four regions all identical -
0x00900000 - 0x0093ffff
0x00940000 - 0x0097ffff
0x00980000 - 0x009bffff
0x009c0000 - 0x009fffff
You should be able to test this quickly with a debugger or uboot (mm, md commands).
Regards
Ross