The invention includes an apparatus and method for dynamically isolating a portion of a scan path of a system-on-chip. In one embodiment, an apparatus includes a scan path and control logic. The scan path includes at least a first hierarchical level, where the first hierarchical level includes a plurality of components, and a second hierarchical level having at least one component. The second hierarchical level is adapted for being selected and deselected such that the second hierarchical level is active or inactive. The control logic is adapted to filter application of at least one control signal to the at least one component of the second hierarchical level in a manner for controlling propagation of data within the second hierarchical level independent of propagation of data within the first hierarchical level. In one embodiment, when the second hierarchical level is deselected, the control logic prevents data from being propagated within the second hierarchical level while data is propagated within the first hierarchical level. In one embodiment, the second hierarchical level may be used for independent, parallel testing while data continues to be propagated through the first hierarchical level.