We can have earthquakes...
What happens during an earthquake? The ground shakes in a way so that the viscosity becomes evenly distributed about the realm! Add up the visc in all of the scenes (except for ones in NML), divide by number of scenes (except ones in NML) and then set the visc at every scene to that amount. Why ignore NML? Because visc there can't be above 0 so it would artificially skew the global results.