Decoupling capacitors work best when they're as close as possible to the pins of the IC (some ICs even have internal decoupling capacitors placed directly on top of the silicon die itself). A capacitor providing decoupling to one chip will not necessarily be adequate decoupling for another chip a few inches away, even if it's nominally enough capacitance for them both.
At low frequencies (e.g. when measured with a multimeter), two capacitors associated with different chips will indeed measure as the sum of their capacitances. But at higher frequencies the impedance of the connecting traces (which is most of the reason these capacitors are used!) will become significant.
Outside of the outputs of amplifiers, it's unusual for too much capacitance to cause a problem, especially if it has significant series impedance (due to being halfway across the board). Note that linear regulators are amplifiers and can exhibit this type of instability, though modern ones are typically more tolerant of large output capacitances. Switching converters, as long as they use some form of soft-start, are unlikely to go unstable, though the cheapest ones might have issues starting up into a 10 mF load.
Decoupling capacitors halfway across the board are not generally something you will need to worry about for any chips other than your PMICs, and then only in fairly extreme cases.
Also, you're extremely unlikely to be using 10 pF capacitors for decoupling. It's usually 100 nF for most chips, a few to a few dozen μF for regulators, and probably somewhere in the 1 to 100 nF range for complex CPUs and FPGAs (times a lot, for the dozens of power supply pins that need decoupling).