1. A method of multiphase flow upscaling of a fine scale geologic model, comprising: from the fine scale geologic model, defining a local domain for generating a dynamic pseudo-function, the local domain including an upstream coarse grid domain adjacent a downstream coarse grid domain, and a concatenated domain adjacent the upstream coarse grid domain, the local domain being configured such that fluid flow to be modeled therethrough flows first through the concatenated domain, then through the upstream coarse grid domain, and lastly through the downstream coarse grid domain, wherein a coarse grid interface is defined between the upstream coarse grid domain and the downstream coarse grid domain; imposing a constant pressure boundary condition of P=1 and a saturation condition of S d =1 on an upstream face of the concatenated domain; imposing a constant pressure boundary condition of P=0 and a saturation condition of S d =0 on a downstream face of the downstream coarse grid domain; imposing a no-flow boundary condition on faces of the concatenated domain, the upstream coarse grid domain, and the downstream coarse grid domain parallel to a direction of fluid flow; simulating fluid flow through the local domain for a plurality of time steps until the local domain is completely flooded; at each time step, recording a fine scale solution of saturation and flow rate of individual fluid phases across the coarse grid interface; constructing a pseudo-function by post-processing results of the simulation of fluid flow; and upscaling the fine scale geologic model to a coarse scale geologic model using the pseudo-function.