How to drop a DB2 instance if instance owner does not exist anymore

Let's say that your instance owner was user db2inst1 and you removed it via OS tools. When you want to uninstall DB2 it complains that you have to drop db2inst1 instance. Running db2idrop gives you error, since user db2inst1 does not exist anymore. In this case you can use this:

db2greg -delinstrec instancename=db2inst1

db2greg is a nice tool that lets you display and alter global registry. More at DB2 10.1 Info Center