There are two primary forms of intents you will use.
Explicit Intents have specified a component (via setComponent(ComponentName) or setClass(Context, Class)), which provides the exact class to be run. Often these will not include any other information, simply being a way for an application to launch various internal activities it has as the user interacts with the application.
Implicit Intents have not specified a component; instead, they must include enough information for the system to determine which of the available components is best to run for that intent.
Maybe we need to find the component name...if there is one.
Also, if we look through the xml files for the system apps we should be able to find which component is listening for ACTION_MEDIA_SCANNER_SCAN_FILE
Frankly, I am out of my depth, because on Java, this is a top-level intent i.e. the android system can understand this, but it seems it is not available in B4A.
On the other hand it would be easy to write a library for this (which i know nothing about!)