I don't know any specifics about Oman. When we need to figure out what region a cache belongs to in order to see how many regions you have logged caches in and what badge you should have, we need to have map data for that country in order to know what caches belong to what region (unless geocaching.com has region information for that country, which isn't that often).
Our map data almost always comes from OpenStreetMap. If there are problems with that data, the same problems will appear in our region divisions, and we normally won't notice by ourselves since we don't have detailed geographical knowledge about all countries in the world.
It is helpful to know that these problems exist (so do tell us!), but in many cases we can't do much to fix them apart from checking to see if the OSM data is better now than when we imported it for that particular country. If you are really interested in fixing this kind of problems, your best option is to help OpenStreetMap make the map better and when it is corrected, tell us to re-import the data for that country.
On http://project-gc.com/Home/CountrySupport you can see what countries have region support from geocaching.com ("Regions") and what countries have map data in our database ("Improved regions").