There are two cases where it is beneficial to flush or clear data without overhead : registers and data memory.

Register set protection

Registers would need to be flushed when calling an unsafe/unvetted module. In this case, it's a per-register attribute that can be set, for each globule, to mark the 4×16 registers as "trap on read" to prevent leaks without writing each register individually. The mark can be removed by writing a new value to the register. This is also a nice safety feature during debugging : the trap can be hooked to help trace a bug for example.

Memory initialisation

A whole cache line (256 bits ?) and even a whole page could be marked as "RAZ" to speed up initialisation. All the bytes get marked as "dirty" and "cleared", and the whole line gets written back to main memory during a flush/replacement. It is particularly handy for initialising a stack frame during a function call (or flushing it upon return).