Methods and apparatus for efficient scaling of fabric architectures such as those based on PCIe technology, including up to very large fabrics and numbers of hosts/devices for use in ultra-high performance applications such as for example data centers and computing clusters. In one aspect, methods and apparatus for using Non-Transparent Bridge (NTB) technology to export Message Signaled Interrupts (MSIs) to external hosts are described. In a further aspect, an IO Virtual Address (IOVA) space is created is used as a method of sharing an address space between hosts, including across the foregoing NTB(s). Additionally, a Fabric Manager (FM) entity is disclosed and utilized for programming e.g., PCIe switch hardware to effect a desired host/fabric configuration.