Apparatus, systems and methods for clustering multiple PCI Express hierarchies to enable access of components in different hierarchies. Each PCI Express hierarchy includes a root device as well as a cluster port for coupling each hierarchy to each other hierarchy of a physical cluster through a PCI Express switched fabric. Memory addresses and transaction IDs are re-mapped by the cluster port of each hierarchy to partition the PCI Express space of the system of multiple hierarchies. A first portion of the partitioned space is reserved for access to local components within a hierarchy. A second portion of the space is used to access remote components of other hierarchies from within a different first hierarchy. The address and transaction ID values exchanged in such remote transactions are re-mapped and used by the cluster port of each hierarchy to route exchanges between hierarchies using standard PCIe root devices, endpoint devices, and switches.