Does iomem comprehensively list everything that's addressable?

There is an address range here that's not listed in /proc/iomem. But when I tried to read in this address range, I got some values, like 0x000000ab, that indicate that there is something behind this address range.

So my question as the title is: Does iomem comprehensively list everything that's addressable? Could there be something else that's memory-mapped but not listed by iomem?

The environment for this issue is Linux running on a custom made board with an X86 CPU.