Hi,
If the reset signal is send by STM809, it's hard to filter. Because reset pin will be pull down for a long time, not just a glitch.
You can add a capacitor after 4k7 resistor to filter glitch.
The RESET_b pin also has a configurable digital filter to reject potential noise on this input after power-up. The configuration bits are located in the RCM_RPFC register.
Regards
Jing