Does the emission of semen and another viscous fluid due to thinking and itching, without the intention of ejaculation, invalidate the fast?

What happened to you was not masturbation that necessitates breaking the fast, because masturbation is the deliberate expulsion of semen. What you did was an act of scratching the private parts out of necessity, and the emission of semen merely by thought does not invalidate the fast. The other fluid may be madhy (pre-seminal fluid) or wady (thick white discharge).