There is only one file type that uses the .SFCACHE extension:
ReadyBoost Cache File
An SFCACHE file is a cache file used by Windows Vista and 7 that may be created on a flash memory device. It adds additional memory that Windows may access as virtual RAM, which may help improve system performance.
ReadyBoost can be enabled by right-clicking the icon of a flash memory device and selecting "Properties." Then click the ReadyBoost tab and check "Use this device." This will create a temporary file named "ReadyBoost.sfcache" on the flash disk.
Updated: September 27, 2017