Three-dimensional (3D) circuits reduce communication delay in multicore SoCs, and enable efficient integration of cores, memories, sensors, and RF devices. However, vertical integration of layers exacerbates the reliability and thermal problems, and cooling efficiency becomes a limiting factor. Liquid cooling is a solution to overcome the accelerated thermal problems imposed by multi-layer architectures. In this paper, we first provide a 3D thermal simulation model including liquid cooling, supporting both fixed and variable fluid injection rates. Our model has been integrated in HotSpot to study the impact on multicore SoCs. We design and evaluate several dynamic management policies that complement liquid cooling. Our results for 3D multicore SoCs, which are based on a 3D version of UltraSPARC T1, show that thermal management approaches that combine liquid cooling with proactive task allocation are extremely effective in preventing temperature problems. Our proactive management technique provides an additional 75% average reduction in hot spots in comparison to applying only liquid cooling. Furthermore, for systems capable of varying the coolant flow rate at runtime, our feedback controller increases the improvement to 95% on average.