Nope.
When the clock signal is received it means that the components in the critical path have sent the output in the destination, and so the state of the chip is coherent and it starts another step, synchronous across all the chip as the previous.
Using your definition then I can say that a block of procedural code that starts on a single thread as soon as an HTTP request is received, processing it and blocking the thread until the end, is asynchronous because it is an action taken in response to an external stimulus, to use your own words.
But it is simply not true. The mechanism that dispatches the call to start the subroutine is asynchronous, the code itself is synchronous.
I'll take your word for it; we are moving into architecture that sits below my experience now. But we are also below the level of abstraction relevant to the original question, which concerned the design of an API used for communicating with hardware outside the CPU.
Any system that shares a clock is synchronous. Two common communication methods for hardware are SPI, which has a shared clock, and is hence synchronous (https://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/SP...) and UART, which has no shared clock, indeed it can be implemented with a single wire, and is hence asynchronous. Internally the receiver's clock needs to be fast enough to correctly sample data being transmitted to it. (Ed: or I guess you might be able to do something clever with an async circuit fed directly by the signaling line.)
Communicating with hardware outside the CPU doesn't have to be synchronous or asynchronous, it's a design decision depending on what you're trying to accomplish. Languages that don't support both methods are missing half of the design space.
