I remove thermal paste using pre-injection swabs which are little pads soaked in IPA as above. They work well but you have to get the worst off manually with something scrapey that won't damage the surface you're working on (plastic spudger is good) and then once it's down to near residue it's worth using some of the above type of swabs. They're particlarly suited as they don't leave bits of lint but be wary that if you do get them there are two types, one is just IPA and other have chlorhexadine or some other antiseptic in which you really don't want to be using as it leaves a residue. You can get them off amazon.
Yes, I use the swabs issued for injecting myself to clean bits of PC. And also bits of motorbike. Occasionally I use them before sticking a syringe in myself.