Hot gas clouds.  The Gas clouds in intergalactic space consist of individual gas atoms (mainly hydrogen and helium), or particles which can have very high energies.  The energy of these gas clouds is expressed as a temperature, the cooler gas clouds consist of neutral atoms, and the hotter clouds consist of gas plasmas, which are the gas atoms stripped of their electrons due to their high temperature, i.e., high energy.  The latter can be at a very high temperature but because the density of these gas molecules in space is so low, the total heat in a given volume is also extremely low, relative to earthly conditions.   Do not confuse the high temperatures of the gas plasmas with the earthly affect of touching a hot object of the same temperature, where the density of the hot object here on earth is billions of times more than the density of a gas cloud in space.  A spacecraft flying through these high temperature plasmas will not melt away simply because the heat available to cause damage is vastly reduced.  The gas molecules are so thin, i.e., widely spaced, that the extreme density of the spacecraft (relative to the plasma) easily absorbs the energy of the small number of gas ions it encounters.  That is not to say there could not be some effect on spacecraft systems but the point is that the amount of heat present in a given volume is not comparable to earthly measures.