Yeah - I had one under an 18x18 on Trammel Ocarina Island last month. Luckily it was only a level 4.
You have two main options.
- Put it back into your chest or Davies Locker for over 30 days, and it will reset. When it resets, it will tell you it's having trouble reading the map - just go open other maps and a few minutes later you'll be able to decode it again for the new location. (note this requires having cartography on you)
- If you don't want to wait, just get rid of it (toss it in luna or brit garbage for cleanup points, or donate to brit library for library points).
- Outside chance - not bloody likely in fel: If you can get access to a Castle, to enter it, you might be able to dig it from the interior courtyard - though given the cramped confines, that might not be very safe even in Trammel.
I happened to catch the owner of the offending house in my instance at home, and gave it to him to see if he could dig it with his T-hunter. He thought it was cool that he had a map for his house location.