1. A method for facilitating selective prefetching based on system resource availability in a computer system, comprising: while executing instructions in a processor, monitoring the availability of at least one system resource and dynamically adjusting an availability indicator for the system resource based on a current availability of the system resource; upon executing a prefetch instruction which generates a prefetch request that involves the system resource, checking the availability indicator; and determining if the availability indicator indicates that the system resource is sufficiently available; if the system resource is sufficiently available, sending the prefetch request; otherwise, if the system resource is not sufficiently available, examining a conditional field in the prefetch instruction wherein the conditional field indicates that the prefetch request should be sent to the system resource despite the system resource not being sufficiently available; if the conditional field indicates that the prefetch request should be sent to the system resource, sending the prefetch request despite the system resource not being sufficiently available, otherwise, terminating the prefetch request; whereby terminating the prefetch request prevents prefetch requests from overwhelming the system resource.