Watchdog timer hierarchy

In one example of the technology, via a first independent execution environment of a set of independent execution environments in an integrated circuit, a first watchdog timer is caused to reset on a periodic basis. The set of independent execution environments is configured to have a defense-in-depth hierarchy. The set of independent execution environments includes a first independent execution environment and a second independent execution environment. The first independent execution environment is a most trusted execution environment on the integrated circuit. Via the second independent execution environment: a second watchdog timer is periodically caused to reset on a periodic basis. In response to the second watchdog timer timing out, an interrupt is communicated from the second watchdog timer to the first independent execution environment. In response to the first watchdog timer timing out, at least a portion of the integrated circuit is reset.