Hi!, i use regular alcohol 96% to clean new and old resine an d flux from PCBs, the key to success here it's time, very volatile solvents like hexane or thinner evaporates before flux starts to dissolve, so you got to protect it from air, i do so by wetting a piece of cotton and applying it over the board and wait a while, old fluxes require more time.
In case a white layer still on the pcb (it's only the dissolved flux) , you must repeat the process with a new piece of cotton and voilá! . You could use a nylon brush in hard cases previous wetted with alcohol.
In other times i've used a contact cleaner from Philips, that do the same job in much less time, but i think they don't produce this spray anymore. The one i mention has a clear smell of turpentine.