1. A method to identify clock cycles that involve switching activity levels that are more likely to result in IR drops that utilize detailed IR drop analysis, wherein the design includes a nonuniform power grid that includes a first power grid region having first physical characteristics and having a second power grid region having a second physical characteristics, the method comprising: using a computer system to run a simulation model of the integrated circuit to simulate scan mode operation of a circuit design during multiple clock cycles; capturing value changes of sequential logic in the course of the multiple cycles; obtaining respective value change count thresholds for respective power grid regions of the non-uniform power grid based at least in part upon the physical characteristics of the respective power grid regions; and determining clock cycles during scan mode operation during which respective numbers of value changes per clock cycle within one or more respective power grid regions meet respective value change thresholds for the one or more respective regions.