So what marvel likes to do is fire up an event, spin off new titles, if they pan out, they hen change the other lines to match it. If it doesn't then they retcon it, or say it happened in an alternate universe. For that reason its actually really hard to say how many times they have done it (DC just retcons everything to say all of it has always happened which is kind of lame, kind of cool).
Off the top of my head 2015 with Secret Wars 2
Marvel Legacy in 2017
Marvel Civil war was a reboot event of sorts, but it was odd. (I have no idea if Civil War 2 was supposed to be)
One of the things they like to do is reboot individual lines, or a group of lines. Which also muddies the waters on counting a grand total of times