Is a specific voltage required for a specific frequency (in processors)?
This is not really complicated, but rather complex. Roughly speaking, the speed (running frequency) of a processor depends on switching speed of logic gates. The switching speed, in turn, depends on driving strength of transistor pairs, which must drive connected nets. The nets have certain capacitance, so with the higher voltage rail the voltage (switching) threshold gets reached faster (since transistor's thresholds are fixed in a particular manufacturing process), so the gate delay is smaller, and pipelines can run faster. 

However, with higher switching voltage the gate would dissipate more (as a function of V^^2), so the die can overheat, which has opposite effect, it slows the switching speed down, and also can destroy the logic unit, say by drastically increase electromigration rate. This imposes upper limit on voltage-speed relationship. 

In the idea of dynamic "scaling", some blocks of CPU (like cache/memory controller) can be configured on fly to run faster, which need higher voltage. So the idea is that every important logic block has an internal LDO power sujpply, and a variable clock control unit. If there is a demand for faster execution of this unit, an auxiliary processor called "PMU", Power Management Unit, would raise the corresponding voltage, then increase its running clock. When demand goes down, the PMU drops the clock first, then reduces the voltage. And PMU microcode monitors temperature of blocks as well.

In short, for every reasonable voltage level there is certain maximum clock rate when the logic can operate without timing errors. Lower clock rate is usually okay, but one can optimize the block for running at lower voltage, which has power saving advantages (like less leakage). On bottom end, if the voltage is set too low, the operating frequency can be zero, so the logic can only maintain flip-flop states, but can't switch.