If mold is on the joist that would be no problem to clean, just needs some equipment and on the sub floor i believe pending on how severe it is you may just get away with a cleaning with specialized chemical thats stronger than bleach (I know the name but cant remember how its spelled) , as well as a negative air machine, some duct tape, plastic sheething, tyvek suits, gloves and other ppe needed for the workers or it could be severe enough that the floors would have to come up (I know you dont like the sounds of that) and possibly trace it up the walls if any moisture wicked its way up sheetrock and the insulation thats in the walls?...

There are special primers for the walls to encase the cat (or dog) smell from this--which is an option.With a floor like this, with about a million high heel divots from 1890 until yesterday, and a finish that has reached the end of its service life, the discoloration is not such a problem, if you intend to put in pet resistant carpet and padding, it will be covered.An alternative would be to sand it down and refinish it to look like a refinished floor...they never look like new because they use chemical clear coats now vs Varnish or shellac like the olden days.Even with sanding the dog stains may need to be bleached out, and may still have trace shadow that they were there.Why is it a computer nook, well it doesn't have to be.

Bleach itself is 99% water.

We actually have the tenants sign a mold addendum that explains how they are responsible to keep mildew or mold at bay by running exhaust vents when showering, treating visable mildew in window sills and bathrooms with bleach, cleaning the AC drainline, running AC when humidity is high ect... 

It’s old nug hugger Levi’s with holes , worn out nikes and a beatup sweatshirt with bleach stains .

The sun had bleached some of them to be unreadable they were out for so long.

Ice, vinegar, lemon peels, bleach treatment for garbage disposer.Inspect septic tank if you have one.Ceiling light fixtures and fans probably have dead mosquitoes and other bugs up there, clean that glass shade or at least use a compressed air canister to blow them out.

I've heard that in many cases it can just be cleaned up with bleach water and the area painted over with Kilz.

Those things grow like weeds - you can almost water them with bleach and have them still grow.

I washed ours 2x before putting them on.Sheet washing - NEVER use bleach in the wash.