I had situation recently where I was deep in some code, manager went and asked about a problem in second unrelated project. Switching mentally between those two

I had situation recently where I was deep in some code, manager went and asked about a problem in second unrelated project. Switching mentally between those two codebases was almost painful and I probably looked quite funny for several seconds. The problem for me is that I've contributed to several different projects in different languages and I'm the most knowledgeable person in my (small) company, so If anyone has problem or doesn't know something, he must ask me. Recently I've found a good way to tame this a little. Asking person is required to write my response in apropriate wiki so that if something was unclear, knowledgebase will be upgraded for everyone.