Imagine if you will, that an Internet meme spread where people were encouraged or challenged to "noogie" the Justin Bieber (aka, give him a friendly knuckle rub on the top of his head). Let's say it became something that every Bieber fan or foe wanted to try. Let's say that it had become a problem.
Now let's say Justin is coming to your town and you have been hired as head of security. How would you deal with this threat? Would you spend time sending all your security personnel all over the city trying to sniff out those noogie-seeking Justin fans? Would you send your best people driving down alleyways and around high-schools in the hopes of maybe, just maybe, finding someone wearing a "Noogie Bieber" t-shirt? Or, would you focus your efforts and put all of your security personnel around Justin Bieber to deal with those crazed fans who were actually getting close enough to the Bieb to try a noogie?
Of course, it would make no sense to spend energy looking for those people that MAY be around and MAY be a threat. It would make perfect sense to focus manpower and energy into surrounding the object of desire and protecting him from actual harm from known threats.
Ok, follow me now. Your scalp is the Bieb. Your home is the city. Lice don't want to hang out anywhere in your home, except on your scalp. And if they do leave the scalp, they are probably not well enough to return. To quote this research, "In addition, fully active lice usually do not leave the head without any reason. Lice leaving the head may be close to dying, and it can be assumed that a high fraction of lice found off-head are not capable of infesting a person or surviving for very long".
So, it is highly unlikely that the lice will be anywhere else, but even if you had the possibility of having lice throughout your home, most of them would never even be able to get to your head. It's a waste of time to try and find these lice. And if by chance, they got to your head, so what? If you put your attention on combing the head, you will stop that louse in its tracks. So, I beg you to stop the house cleaning and excessive laundering. Focus your precious time and energy on the heads in the house.