Hi stefanm38281801,
There isn't an equivalent to clearVars in GA, but the persistence of certain variables is treated differently in GA vs Adobe. What I assume you are doing is setting the Custom Dimension within the Custom Dimensions and Metrics section of the event based rule. What this section does is sets the dimension globally for any beacons that are sent from the page after the value is set. Setting a Custom Dimension here is the equivalent to calling:
ga('set', 'dimension1', 'A');.
To have a more locally scoped Custom Dimension where it only applies to a specific GA Event you want to use the Parameters section of the Events area. Here you can set parameters such as Custom Dimensions, Custom metrics, etc. and those will only apply to that event beacon and shouldn't be inherited by any subsequent beacons. Equivalent code of what setting a CD in Parameters looks like:
ga('send', 'event', 'eventCategory', 'eventAction', {
'dimension2': 'B'
});

GA documentation for reference: Custom Dimensions and Metrics | Analytics for Web (analytics.js) | Google Developers