Here we demonstrate an 8x4 multi-wavelength selective ring resonator based crossbar switch matrix implemented in a 220-nm silicon photonics foundry for interconnecting electronic packet switches in scalable data centers. This switch design can dynamically assign up to two wavelength channels for any port-port connection, providing almost full connectivity with significant reduction in latency, cost and complexity. The switch unit cell insertion loss was measured at 0.8 dB, with an out-of-band rejection of 32 dB at 400 GHz channel separation. All the ring resonator heaters were thermally tuned, with heaters controlled by a custom 64-channel DAC driver. Detailed measurements on the whole switch showed standard deviation of 2 dB in losses across different paths, standard deviation of 0.33 nm in resonant wavelength and standard deviation of 0.01 nm/mW in ring heater tuning efficiency. Data transmission experiments at 40 Gbps showed negligible penalty due to crosstalk paths through the switch.