Millimeter wave (mmWave) communications has attracted significant attention due to its potential for providing very large bandwidths. Unfortunately, the propagation of millimeter waves suffers from severe path loss and blocking, which limits the coverage of mmWave systems. To overcome this, mmWave hotspot empowered two-tier heterogeneous networks are expected to play an important role in the sixth generation (6G) of mobile communication systems. When the deployment of mmWave hotspots is not dense enough, or even sparse, assuring the quality of service (QoS) for mobile users becomes rather challenging. In this paper, we present a mobility-enabled pushing scheme, in which popular content items are cached by a mobile user when he/she can be served by an mmWave hotspot. Optimal pushing policies with statistical mobility models and predeter-mined trajectories are presented and analyzed respectively. Both theoretical and numerical results demonstrate the substantial caching gain due to user mobility in mmWave hotspot empowered two-tier networks.